The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment the present invention is related to heat fusible encapsulated toner compositions comprised of a core containing pigments or dyes, and wherein the core is encapsulated in certain modified polyesters, especially amorphous polyesters derived from reactive or telechelic polyesters. Also, the present invention is directed to an economical and flexible process for the in situ formation of telechelic polyesters which can then be transformed to the modified polyester shell components having various desirable thermal, triboelectrical and morphological properties. More specifically, the shell formation process of the present invention in one embodiment is directed to a two stage interfacial condensation polymerization which can be adapted for the preparation of amorphous, liquid crystalline and semicrystalline polyesters or polyarylates with various specific chain ends, molecular weights and structures such as block and branched polyesters. Also, with the present invention toner particles of an average volume diameter of from, for example, 5 to about 30 microns with narrow size distributions of from, for example, about 1.3 to 1.8 can be obtained, and classification is eliminated. Further, there is provided with the present invention a process for the preparation of various colored toners from laboratory scale (less than 1.0 kilogram) to large scale toner production (up to several hundred kilograms). Another specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core containing polymer binders, and dye or pigment particles, which core is encapsulated by modified polyester shells. Advantages associated with the toner compositions of the present invention include the elimination and/or the minimization of image ghosting; excellent toner fixing characteristics; superior surface release properties enabling their selection, for example, in imaging and printing systems wherein a release fluid such as a silicone oil is avoided; substantially no blocking or agglomeration of toner particles; excellent toner powder flow characteristics without surface additives; no leaching of the core components or complete encapsulation; low processing costs, heat fusing characteristics and properties that approximate those of the conventional toner compositions; and the capability for lower melting core materials, controlling and altering the weight average and number average molecular weight of the shell polymers and the structures thereof by, for example, selecting various end capping components thereby providing, for example, acceptable surface properties including desirable charging characteristics, excellent flowing toners, hydrophobicity of the toner particles, and the like; complete shell formation wherein contamination is avoided and/or minimized; and encapsulated toners, which evidence a high degree or percentage of pigment dispersion. Also, and more specifically, the toner compositions of the present invention possess core melting temperatures as low as 50.degree. C. and shell weight percent as low as 5 percent, permit a life extension of the fuser roll incorporated into, for example, electrostatographic, especially xerographic, imaging processes in that, for example, lower fusing energies can be selected, that is fusing can be affected at temperatures not exceeding 140.degree. C. in many embodiments. One of the primary purposes of encapsulation for the toners of the present invention is to passivate the pigment charging, that is the charging characteristics of the toner particles are ultimately controlled by that of the colorants, especially those exposed at the surfaces of the toner particles. Influence of the pigment charging can be prevented by encapsulation of various color particles with a common shell modified polyester polymer of the desired charging properties. Thus, for example, the toner compositions of the present invention can be charged positively or negatively in a narrow tribo range of less than 10 microcoulombs per gram, and preferably below 5 microcoulombs per gram, irrespective of the pigment type selected for the core. Therefore, developer charging, including triboelectric and admix characteristics, can be controlled and preselected with the process of the present invention, including the use of a surface additive in conjunction with appropriate carrier particles. Moreover, the toner particles obtained by the process of the present invention are environmentally stable due partly to the hydrophobicity of the polyester shells, and homogeneous or high degree of pigment dispersion without agglomerated pigment particles within the core. As a result, images with high color chroma and high transparency projection efficency can be achieved with the toners of the present invention.
The toner compositions of the present invention can be selected for a variety of known reprographic imaging and printing processes including electrophotographic and ion printing (ionography) processes. They can also be utilized in electrophotographic copying and printing apparatus wherein the transfer of developed images onto paper is executed electrostatically, and the subsequent fixing of transferred images is accomplished by application of pressure, thermal energy or a combination of pressure and thermal energy. The toner compositions of the present invention provide excellent surface release characteristics, and the use of lubricating silicone oils or other surface release fluids to prevent image offset to the pressure roll and hot roll fuser can be avoided.
The toner compositions of the present invention can in one specific embodiment be prepared by first mixing colorants, preformed core resins, a mixture of core monomer liquids, oil-soluble shell monomers, free radical polymerization initiators, and additives such as plasticizers, pigment dispersants and chain transfer agents to provide a pigment dispersion mixture; dispersing the pigment dispersion into an aqueous emulsifier or stabilizer solution containing a phase transfer catalyst under high shear to yield a suspension of pigmented droplets; adding an aqueous solution of water-soluble shell monomers to the resulting suspension to react with the oil-soluble shell monomers to form a reactive polyester shell around the droplets; adding another aqueous solution containing a preselected nucleophile to react with the reactive polyester and provide the final shell components; heating the resulting suspension to accomplish radical polymerization of the core monomers; washing the resulting toner particles with water; and spray or freeze drying the washed particles to allow the final encapsulated toner product.
In the present invention, shells for the cores are obtained by known interfacial polymerization processes or more specifically by a two stage interfacial polycondensation which is based upon the control of the stoichiometric balance between the oil- and water-soluble shell monomers. Preparation of reactive or telechelic polymers through interfacial polycondensation of nonstoichiometric balanced monomers is well known, see Nguyen, H. A. and Marechal, E. Review of Macromolecular Chemistry and Physics, 1988, C28(2), 187 to 291; and Percec, V.; Coleen P.; Pask, S. D. in Comprehensive Polymer Science, 1989, vol. 6, chapter 9, Allen, G. Editor, the disclosure of which is totally incorporated herein by reference. Of background interest is the article "Synthesis of Block Copolymers via Two-Step Interfacial Polycondensation", Tsai, H. B. and Lee, Y. -D. Journal of Polymer Science Polymer Chemistry Edition, 1987, 25, 3405 to 3412, the disclosure of which is totally incorporated herein by reference. This article discloses that a reactive polyester with carboxylic acid chloride end groups was obtained within ten minutes when the molar ratio of bisphenol A to a diacid chloride was less than one. In the second stage, the reactive polyester was reacted with additional bisphenol to provide a final polyester with increased molecular weights.
Encapsulated toners with polyester shells are well known. There were recited in a patentability search as prior art U.S. Pat. Nos. 4,699,866 directed to encapsulated toner materials with improved powder characteristics, see for example the Abstract of the Disclosure, and wherein the shell material can be selected from a variety of resins including polyesters, reference column 3, beginning at line 19, and wherein encapsulation can be accomplished by interfacial polymerization, reference column 3, beginning at line 29, to column 4, line 18, for example, the disclosure of the aforementioned patent being totally incorporated herein by reference; 4,774,160 directed to toner compositions with amorphous ternary copolycarbonates, reference for example the Abstract of the Disclosure and column 5, although there does not appear to be any teaching in this patent with respect to encapsulated toners; 4,049,477 directed to finely divided toner particles comprising a colorant in an amorphous low melting aromatic polyester wherein the polyester contains within the polymer chain at least 30 mol percent of at least one divalent radical, reference the Abstract of the Disclosure, and wherein the polyesters can be prepared by any conventional condensation or transesterification polymerization process, reference column 5, beginning at line 56, however, it does not seem to be any mention of encapsulated toners in this patent; and 4,758,506 directed to encapsulated cold pressure fixable toners comprised of a core containing magnetite particles and a styrene butadiene styrene block polymer and a polymeric shell material generated by an interfacial polymerization process, see the Abstract of the Disclosure, and note column 5, beginning at line 46, wherein it is indicated that the shell materials can be prepared by interfacial polycondensation processes as disclosed, for example, in U.S. Pat. No. 4,000,087, and wherein polyamides, polyureas, and polymeric shells are mentioned, see column 5, beginning at line 52. Also known are thermotropic liquid crystalline polymers, especially polyesters, as shell materials for heat fusible encapsulated toners, however, the aforementioned polyesters are considered costly and the formation of these shells with reasonable desired molecular weights have in some instances not been readily achievable. With the present invention, in some embodiments, there are selected as the shell low melting amorphous polyesters derived from economical and expensive diacid chlorides, such as phthaloyl, isophthaloyl, or tetraphthaloyl dichlorides and the corresponding halides and bisphenols such as resorcinols, hydraquinones, bisphenol A, bisphenol F, and the like.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 encapsulated electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483. In U.S. Pat. No. 4,803,144, there is enclosed microcapsule toners obtained by interfacial polymerization microencapsulation process wherein a preformed polymer is employed as the core binder. The process of this invention also involved the use of suitable low boiling solvent to dissolve the polymer binder, and to promote the interfacial polymerization process.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in application U.S. Ser. No. 718,676 (now abandoned), the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
There are disclosed in Konishiroku Japanese Publications Nos. 60/198554 A2, 60/198555 A2, and Canon Japanese Publication No. 61/65260 A2 heat fusible encapsulated toner compositions in which the shell of the encapsulated toner is prepared by an overcoating process involving the use of an organic solvent and polymeric materials of high melting points with a sufficient glass transition temperature to provide good blocking properties for these compositions. In contrast to the processes disclosed in the Japanese publications, the shells of the present invention can be prepared by interfacial polymerization in a simplified continuous one step process wherein the core and the shell of the toner are simultaneously formulated, which process therefore is of lower cost, that is from about 15 to about 40 percent less than the aforementioned prior art processes.
There is disclosed in Japanese Publication No. 61/56352 A2 heat fusible encapsulated toner compositions with a core prepared by in situ free radical polymerization with an epoxy-urea shell of a very high melting temperature. These toners do not ordinarily possess low melting properties, that is they usually cannot be heat fixed with fusers set at temperatures as low as 120.degree. C. In contrast, the toner compositions of the present invention can be used both in conventional heat fusing imaging systems wherein high melting materials with, for example, a softening point above 100.degree. C. are required necessitating fuser temperatures of up to 180.degree. C., and in low melt applications as the shell and the core can be formulated accordingly.
Additionally, there are disclosed in Japanese Publication No. 61/118758 A2, Japanese Publication No. 59/218460 A2, Japanese Publication No. 61/28957 A2, Japanese Publication No. 60/175057 A2, and Japanese Publication No. 60/166958 A2 heat fusible toner compositions prepared by suspension polymerization. Examples of patents illustrating colored photocapsule toners include U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483. More specifically, the '483 patent illustrates encapsulated toner materials which have applications in very specific areas such as pressure sensitive recording paper. Capsules prepared for this application are usually coated on a substrate directly from the emulsion in which they are prepared and withstand with difficulties spray drying processes, a disadvantage alleviated with the toners prepared in accordance with the process of the present invention. Furthermore, these capsules contain an organic liquid in the core which, when used in a dry development system, could result in poor fix properties. Also, the range of particle sizes prepared by the aforementioned prior art process results in the formation of pressure sensitive recording particles which are usually not acceptable for electrostatographic development systems.
Moreover, there is described in U.S. Pat. No. 4,476,211, the disclosure of which is totally incorporated herein by reference, the preparation of electrostatographic toner materials with surface electroconductivity. Specifically, there is disclosed in the '211 patent a cold pressure fixable toner composition with polyamide, polyurea and other types of shell materials prepared by an interfacial polymerization process. The colorant selected for these compositions is generally comprised of a variety of dyes or pigments, and the core contains a polymeric material with a binder therein for retaining the colorant within the core and assisting in the fixing of the colorant onto the surface of a support medium. Examples of high boiling liquids selected for the process of the '211 patent include those boiling at temperatures higher than 180.degree. C. such as phthalic esters, phosphoric acid esters, and alkyl naphthalenes.
Also, there are illustrated in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of resin particles selected from the group consisting of thermotropic liquid crystalline polycarbonates, copolycarbonates, polyurethanes, polyesters, and copolyesters; and pigment particles. The aforementioned thermotropic liquid crystalline polymers, especially the polyesters and the polyurethanes, are useful as shells for the toner compositions of the present invention. However, the toner compositions of the '313 patent are not encapsulated and are prepared by conventional processes, such as melt blending and jetting.
Disclosed in application U.S. Ser. No. 043,265, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of core components, and thereover a thermotropic liquid crystalline polymeric shell formulated by interfacial polymerization. Further, in this application there is described black or colored toner compositions comprised of a polymer core or polymer mixtures, and pigment particles encapsulated in a shell formulated by interfacial polymerization processes, which shell is selected from the group consisting of thermotropic liquid crystalline polyesters, polycarbonates, polyurethanes, copolycarbonates, and copolyesters, reference the aforementioned U.S. Pat. No. 4,543,313. Therefore, in one specific embodiment of the aforementioned application the toner compositions are comprised of a polymer core having dispersed therein as pigments components selected from the group consisting of black, cyan, magenta, yellow, red, magnetites, and mixtures thereof; and thereover a thermotropic liquid crystalline polymeric shell. Also, additive particles in an amount of from about 0.1 percent by weight to about 1 percent by weight, such as colloidal silicas, inclusive of Aerosils and/or metal salts, or metal salts of fatty acids, inclusive of zinc stearate can be added to the formulated encapsulated toner. Moreover, there can be incorporated into the toner compositions of the copending application charge enhancing additives in an amount of from about 1 percent to about 20 percent by weight to enable positively charged toner compositions, which additives include alkyl pyridinium halides, reference U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference; sulfate and sulfonate compositions, reference U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference; distearyl dimethyl ammonium methyl sulfate, reference U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference; and the like. Furthermore, there are provided in accordance with the copending application processes for the preparation of toner compositions wherein the shell component is obtained by interfacial polymerization.
In one preferred specific embodiment of the aforesaid copending application, there are illustrated toner compositions comprised of a core of (1) a pre-polymerized styrene-n-butylmethacrylate copolymer with a glass transition temperature of about 55.degree. C. present in an amount of from about 1 percent by weight to about 30 percent by weight, and preferably from about 10 percent by weight to about 20 percent by weight, and an in situ polymerized styrene polymer present in an amount of from about 30 to about 50 percent by weight of the toner; and (2) a mixture of magnetite, from about 1 percent to about 60 percent by weight, and preferably from about 1 percent to about 30 percent by weight, and carbon black from about 2 percent to about 15 percent by weight, and preferably from about 3 to about 10 percent by weight, encapsulated with a polyester thermotropic liquid crystalline shell present in an amount of from about 10 percent to about 25 percent by weight. The resulting toner has a core/shell morphology with a shell thickness of from about 0.05 to about 1.0 micron. With further respect to the specific aforementioned compositions, there can be present in the core either carbon black or magnetite in an amount of from about 3 to about 8 percent, and from about 15 to about 20 percent, respectively.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676 relating to cold pressure fixable toners, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.